Tool strings conveyed in wellbores in the course of constructing and maintaining oil and gas wells may range in length up to several hundred meters. Deploying a longer tool string into a pressurized wellbore may utilize one or more deployment bars between shorter, more manageable sections of the tool string. However, this technique is not available when there are two flowpaths, such as a first flowpath for pressurized fluid being pumped through the tool string and a second flowpath for fluid flowing out of the wellbore to surface equipment. That is, the two flowpaths cannot be adequately isolated from one another as the tool string is incrementally assembled and deployed into the wellbore.